The invention relates to an internal combustion engine and, more particularly, to an exhaust system having a first and a second exhaust gas turbocharger for an internal combustion engine with eight cylinders in a V-design, a first cylinder bank being formed by a first, a second, a third and a fourth cylinder arranged in series side-by-side, and a second cylinder bank situated opposite the first cylinder bank being formed by a fifth, a sixth, a seventh and an eighth cylinder arranged in series side-by-side.
German published patent application DE 10 2004 057 129 A1 describes a V-engine having 8 cylinders (a V8 engine) with an ignition sequence (or firing order) of a 90° crank angle from one cylinder to the next. Each cylinder bank of the internal combustion engine has four cylinders. Two cylinders respectively of a cylinder bank lead into an exhaust line which, in each case, conducts the exhaust gases of the four assigned cylinders into an exhaust gas turbocharger. The internal combustion engine therefore has two four-flow exhaust lines. Together, the two exhaust lines form an exhaust system. Before entering into the turbochargers, the exhaust lines can be connected with one another in an exhaust-gas-carrying manner. One emission control system respectively is arranged in the exhaust system behind each exhaust gas turbocharger in the flow direction of the exhaust gas.
A disadvantage of the described embodiment is a so-called side-to-side action of the exhaust gases of the four cylinders each leading into an exhaust line, whereby a maximal opening duration of the charge cycle intake valves cannot be implemented.
It is an object of the present invention to provide an exhaust gas system which prevents side-to-side action of the exhaust gases of the four cylinders assigned to an individual exhaust line.
This and other objects are achieved by an exhaust system having a first and a second exhaust gas turbocharger for an internal combustion engine with eight cylinders in a V-design, a first cylinder bank being formed by a first, a second, a third and a fourth cylinder arranged in series side-by-side, and a second cylinder bank situated opposite the first cylinder bank being formed by a fifth, a sixth, a seventh and an eighth cylinder arranged in series side-by-side. The internal combustion engine has an ignition sequence of a 90° crank angle from one cylinder to the next. The exhaust system has a first, a second, a third and a fourth exhaust line from the cylinders to the two exhaust gas turbochargers. Two cylinders are respectively assigned to an exhaust line, and one exhaust turbocharger is respectively assigned to two exhaust lines. The two cylinders assigned to the exhaust line have an ignition interval of a 360° crank angle, and the first and the second exhaust line assigned to the exhaust gas turbocharger have an ignition sequence offset from one another by a 180° crank angle.
As a result of the further development according to the invention, the ignition interval amounts to a 360° crank angle of the two cylinders assigned to an exhaust line or a flow. The turbine wheel of the exhaust gas turbocharger is therefore acted upon by exhaust gases at a 180° ignition interval. By way of this further development, it becomes possible to prolong the opening duration of the charge cycle intake valves in comparison to the state of the art, whereby more power and torque are obtained for the internal combustion engine.
Due to the exhaust system embodiment according to the invention, a better charge exchange is achieved since a symmetrical identical filling with fresh air exists for all eight cylinders. As a result of the symmetrical identical filling, less residual gas remains in the individual cylinders, whereby the knock tendency of the internal combustion engine is significantly improved (knocking is reduced) In addition, fuel consumption is improved, particularly at full load of the internal combustion engine. Furthermore, very high torque values will already exist when the rotational speeds are very low. As a result, the so-called “turbo hole”—a weakening of the torque—in the lower rotational speed range—is almost completely eliminated. Advantageously, the exhaust system according to the invention can be used for internal combustion engines operating according to the spark ignition principle, as well as for internal combustion engines operating according to the Diesel principle.
According to one aspect of the invention, the exhaust system and the two exhaust gas turbochargers are mainly arranged in the V between the cylinder banks. As a result, extremely short paths for the exhaust gas are achieved in the exhaust system. This minimizes flow losses of the exhaust gas and benefits the emissions as well as the fuel consumption.
In a further embodiment of the invention, the first and second turbochargers are twin-scroll turbochargers. This further development is particularly preferred for a two-flow exhaust gas turbocharger, in which case each flow is acted upon by exhaust gas from an exhaust line.
In a further preferred embodiment, the first exhaust gas turbocharger includes a first turbine wheel and the second exhaust gas turbocharger includes a second turbine wheel. The first turbocharger has a third turbine wheel and the second turbocharger has a fourth turbine wheel. Accordingly, each exhaust gas turbocharger has two exhaust gas turbines which each has a separate flow, one exhaust line respectively leading into each flow.
Further preferred embodiments, or manufacturing variants are described herein.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.